ProSe permits mobile terminals to transmit radio signals directly to and receive radio signals directly from other mobile terminals in proximity thereto. Thus, ProSe includes, for example, device-to-device (D2D) communications. The transmission of radio signals directly between mobile terminals during ProSe operation may be performed under network control, such as in instances in which the radio signals are within the licensed spectrum of a network operator. Alternatively, in instances in which public safety messages are transmitted utilizing a dedicated public safety spectrum, the transmission of radio signals directly between mobile terminals in accordance with ProSe operation may be performed autonomously without network control.
ProSe may operate in any one of a plurality of states, such as an RRC_Idle state, an RRC_Connected state or a hybrid RRC state or sub-state (both of which are referenced as a hybrid RRC herein) that is designed for ProSe purposes and that may include characteristics of both the RRC_Idle state and the RRC_Connected state. For example, in both the RRC_Idle state and the hybrid RRC state, the network, such as an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN), may not create and store context for the mobile terminal, while in the RRC_Connected state the network may create and store context for the mobile terminal. Additionally, the mobile terminal may be synchronized with the network in both the RRC_Connected state and the hybrid RRC state even though the mobile terminal is not synchronized with the network in the RRC_Idle state.
In order to perform ProSe under network control, the network operator and, as such, the cell upon which the mobile terminal is camped must support ProSe operation since, among other reasons, ProSe discovery resources may be allocated on a per cell basis by the network, such as the E-UTRAN. The network may provide the radio resources to the ProSe-capable mobile terminals, such as by session information block (SIB) signaling. Thus, while in the RRC_Idle state or in the hybrid RRC state in which no context information for the mobile terminal is stored by the network, a mobile terminal that is camped in a cell that supports ProSe by providing the necessary radio resources may be able to transmit and receive ProSe discovery messages so as to commence ProSe operation, such as D2D communication, with another mobile terminal.
In an instance in which a mobile terminal that is utilizing ProSe is operating in a state in which the network does not maintain context information for the mobile terminal, such as the RRC_Idle state or the hybrid RRC state, the mobile terminal may perform cell re-selection to a cell that does not provide or support ProSe services. As such, the mobile terminal may be unable to continue ProSe operation following cell re-selection. In this regard, the mobile terminal may be unable to both transmit and receive discovery messages or participate in D2D communication in the cell that does not support ProSe services. Thus, the mobile terminal may be unable to rely upon continued ProSe operation in an instance in which the mobile terminal re-selects to another cell.